The present invention relates to a process and device for the injection-molding of plastics by introducing the injection molding material into a mold through various entry gates.
Processes for the injection-molding of plastic materials by introducing the plastic into the mold through various gates are already known. In these processes the injection mold is filled by supplying the plastic melt simultaneously through the various gates with the advancing fronts of the melt, which extend from each gate, subsequently merging in the mold.
The ultimate strength of such an injection-molded article is less at the weld lines which develop between the melt fronts than at locations away from the weld lines. Moreover, the weld lines frequently remain visible on the article, which renders the article visually unattractive.
An already-known process for the manufacture of thin tubes, such as full length Foley catheters, is described in U.S. Pat. No. 4,041,122, wherein melt material is successively let into a mold through various inlets. In such process, material can initially enter the injection mold from one gate proximally of a follower but enters through other gates only after the slidably disposed follower, or follower(s), located on a wire insert has (have) been pushed past the subsequent gates by the molding material which was injected through the first gates.
The present invention provides a process for injection molding plastics in which the material to be injection-molded is controllably introduced into a mold in the absence of any follower, and through various gates or apertures whereby the aforementioned drawbacks are overcome.
The process is quite suitable for manufacturing lengthy articles with relatively thin walls such as plastic bumpers and dashboards for automobiles.